Seals and sea lions may be to blame as the origin of tuberculosis in North and South America, a new study by Arizona State University has revealed.

“New research shows that tuberculosis likely spread from humans in Africa to seals and sea lions that brought the disease to South America and transmitted it to Native people there before Europeans landed on the continent,” read a news release sent out by ASU on Wednesday.

Modern strains of tuberculosis found in North and South America are closely related to European strains of the disease, which suggests that Spanish explorers brought the disease to South America in the 16th century.

Before the seal discovery, it was previously believed that that tuberculosis is an estimated 70,000 years old and it was contracted by humans before they left the African continent.

The tuberculosis strains in South America were recently discovered by a team of scientists studying ancient human remains in Peru. The team was lead by Johannes Krause at the University of Tübingen in Germany.

“We wanted to reconstruct the genome of those ancient M. tuberculosis to obtain a sort of molecular fossil,” Krause, a paleogeneticist, explains in the Nature article. “Pathogens don’t leave fossils, but they do leave their DNA in the skeleton, teeth and bones of the victims of the disease.”

Nature reported that Krause and his colleagues did their own calculations to determine the age of the latest strains of tuberculosis, comparing them to the 1,000-year-old strains from the Peruvian remains. Their findings estimate that “most recent common ancestor” of all strains of tuberculosis are less than 6,000 years old.

Tom Gilbert, an evolutionary biologist at the University of Copenhagen, finds the theory that seals gave tuberculosis to humans interesting but said he hasn’t reached the same conclusion.

“What’s more likely — that marine mammals gave rise to tuberculosis in humans in South America, or that we simply haven’t sampled enough relevant terrestrial hosts on the continent to spot the true ancestor?” he said, according to Nature.